1. Field of the Invention
The present invention relates to a bag transfer device used in bag filling and packaging apparatuses and the like and more particularly to a bag transfer device that includes a plurality of pairs of left and right grippers installed on a table rotating horizontally and a spacing adjustment mechanism provided for adjusting the spacing between the left and right grippers.
2. Description of the Related Art
Japanese Utility Model Application Publication No. H5-28169 discloses a bag transfer device that is installed in a bag filling and packaging apparatuses. This bag transfer device comprises an intermittently rotating table and a plurality of pairs of left and right grippers disposed at a constant angular spacing around the table. The left and right grippers are moved intermittently around a circular movement path when the table rotates. Each gripper has an arm and a clamping component installed at the distal end of the arm. The arms of the left and right grippers are axially supported respectively at their base portions by the table, and they are able to pivot in linear symmetry to each other within a horizontal plane.
The above-described bag transfer device includes, as a spacing adjustment mechanism for adjusting the spacing between the left and right grippers, a cylindrical cam, which is installed under the table so as to be able to move up and down, and an L-shaped lever, and it further includes a star cam and a latching pin. The center axis of the cylindrical cam coincides with the rotational axis of the table, and its upper end makes is a cam face. The L-shaped lever is axially supported by the table and is able to pivot in a vertical plane, and it has at one end thereof a cam follower that rotates over the cam face of the cylindrical cam and also has at another end thereof a press roller that comes into contact with the tail end of the arm so as to cause the arm to pivot. The star cam is rotated coaxially with the table. Also, the star cam can be rotated relative to the table and further can be positioned at a position after it has been rotated by a suitable angle. The latching pin is fixed to the arm.
In the above-described bag transfer device, while the table intermittently is rotating, the cam follower rotates over the cam face and moves up and down according to the shape (protrusion) of the cam face, which is accompanied by the opening and closing motions of the arms of the left and right grippers, so that the spacing between the left and right grippers (and especially the spacing between the clamping components) increases or decreases within a specific range. When the spacing between the left and right grippers decreases to a specific value, the latching pin comes into contact with the star cam. The maximum spacing of the left and right grippers is determined by the maximum height of the cam face of the cylindrical cam, and the minimum spacing of the left and right grippers is restricted by the star cam.
When the bag size (and particularly the bag width) is changed (or bags of different sizes are processed by bag transfer device), the maximum and minimum spacing of the left and right grippers has to be adjusted to match the width of the changed (or different) bag. This can be done by raising or lowering the cylindrical cam and rotating the star cam relative to the table.
Japanese Patent Application Laid-Open (Kokai) No. H9-95318 is similar to Japanese Utility Model Application Publication No. H5-28169, and it discloses also a bag transfer device. This bag transfer device includes an intermittently rotating table and a plurality of pairs of left and right grippers disposed at a constant angular spacing around the table. In this bag transfer device, instead of the cylindrical cam and star cam of Japanese Utility Model Application Publication No. H5-28169, a bag width setting cam and an offset width adjustment cam are employed as a spacing adjustment mechanism for adjusting the spacing of the left and right grippers. The offset width is the distance that the clamping components of the grippers are moved, during the process of the table making its intermittent rotation, between the widest and narrowest spacing of the left and right grippers, and it is equal to one-half the difference between the maximum and minimum values for the spacing of the left and right grippers.
Furthermore, in the bag transfer devices disclosed in Japanese Patent Application Laid-Open (Kokai) Nos. H11-189201 and 2007-210646, parallel links are employed as a spacing adjustment mechanism so as to adjust the spacing of the left and right grippers.
In the above-described bag transfer devices of Japanese Utility Model Application Publication No. H5-28169 and Japanese Patent Application Laid-Open (Kokai) No. H9-95318, when a change in bag size (bag width) dictates the adjustment of the spacing of the left and right grippers, the arms are pivoted around their base portions within a horizontal plane. Accordingly, other than the bags of a certain size (width), the clamping faces of the clamping components of the grippers can be tilted with respect to the width direction of the bags, and the gripper spacing becomes narrow to cause deformation of the opening shape when the bag mouth is opened, which may prevent the bags from being filled stably. Meanwhile, when the gripper spacing is increased and the bag mouth is closed, the edges of the bag (the places where the bag is clamped by the clamping components of the grippers) can become tilted, and this would prevent the stable sealing of the bags as well. Also, if the arms are pivoted in a horizontal plane, the clamping faces of the clamping components of the grippers deviate in the bag thickness direction (the radial direction of the table). Accordingly, the transfer path of the bags may vary depending on the bag size (bag width) (in other words, the transfer path of the bags may deviate in the thickness direction of the bags), which may prevent stable processing in, for instance, the opening step, the filling step, and sealing step for the bag.
In the above-described bag transfer devices of Japanese Patent Application Laid-Open (Kokai) Nos. H11-189201 and 2007-210646, the spacing of the left and right grippers can be adjusted by varying the inclination of parallel links that support the clamping components of the grippers, and at that time no tilting of the clamping faces of the clamping components would occur with respect to the width direction of the bags. However, due to the properties of the parallel link, when the spacing of the left and right grippers is changed, the clamping faces of the clamping components deviate in the thickness direction of the bags (in other words, the transfer path of the bags deviates in the thickness direction of the bags), and this movement cannot be restricted.
Also, the above-described problems in tilting of the clamping faces of the clamping components of the grippers with respect to the width direction of the bags or in a change in the transfer path due to deviation of the clamping faces of the clamping components of the grippers in the thickness direction of the bags can likewise occur when the spacing of the left and right grippers is increased or decreased while the grippers are being moved along the movement path.